What are invertebrates?

Characteristic traits of invertebrate animals

They are multi-cellular and all the cells are assigned different tasks

They have no cell walls

They reproduce by two reproductive cells or gametes

Classification of invertebrates

1. Sponges – poriferans

They are known as sponges

They live in salt water fixed to some object

Their body is covered with pores through which their food enters

Example – Sycon, Spongilla

2. Cnidarians

They live in the marine habitat

The body is like a tube with one opening called mouth

Mouth is surrounded by tentacles that help in capturing prey

They have a radially symmetrical body

Example – Hydra, Jellyfish

3. Platyhelminthes – flatworms

They can be found in marine/fresh water

They have flat, ribbon shaped body

The body is bilaterally symmetrical

The body has a single opening

Most of them are parasites

Example – Tapeworms, Liverfluke

4. Nemathelminthes – roundworms

They are found in fresh/marine water or on land

They have a thread like, rounded body

They have an unsegmented body

Their body has two openings, mouth and anus

The body is bilaterally symmetrical

Most of them are parasites and reproduce sexually by laying eggs

Example – Pinworm, Ascaris

5. Annelids – segmented worms

They are found in marine and fresh water

They have segmented bilaterally symmetrical body

They have a body cavity

They have special organs of excretion known as Nephridia

Example – Earthworm, Leech

6. Arthropods – animals with jointed legs

They have a segmented, bilaterally symmetrical body

Their body is divided into three parts – Head, Thorax and Abdomen

It is covered by a tough outer covering called exoskeleton

They have jointed appendages

Example – Ants, Honeybee, Scorpion, Spider

7. Molluscs – soft bodied shelled animals

Animals have a soft unsegmented body with an external hard shell

Example – Squid, Snail, Octopus

8. Echinoderms – spiny-skinned animals

They live in the marine environment and have spines all over the body

The body is radially symmetrical

Their body has two openings, mouth and anus

They have tube like feet having suckers

Example – Starfish, Sea Urchins

5 Fun facts about vertebrates and invertebrates

Different types of vertebrates have different numbers of vertebrae. Humans have 33 vertebrae, an alligator has 66 vertebrae, and a snake has about 500 vertebrae!

Vertebrates have advanced nervous system, therefore, they are much more intelligent than invertebrates.

Invertebrates cannot make their own food, and therefore, they have to feed off other things to get their energy.

Mammals and birds are warm-blooded, which means that they can make their own body heat even when the temperature outside is low. The body temperatures of warm blooded animals usually stay the same.

The body temperature of the cold-blooded animals, like reptiles, fish and amphibians depends on the temperature outside. For example, when the sun sets at night, their bodies become cold and when the sun rises, their bodies become warmer.